Fermat primality test. most applications use a Miller-Rabin or Baillie-PSW test for primality. Sometimes a Fermat test (along with some trial division by small primes) is performed first to improve performance. GMP since version 3.0 uses a base-210 Fermat test after trial division and before running Miller-Rabin tests. Libgcrypt uses a similar process with base 2 for the Fermat test, but OpenSSL does not.